In order to make synchronous switching possible in the operation of a high-voltage power switch fitted with a hydraulic drive by means of a triggering control device (16), the available hydraulic pressure in the hydraulic drive system (2) is used as a correction factor to determine the triggering delay. The hydraulic pressure in the hydraulic system repeatedly falls within a pump cycle (12) to a minimum, to be brought up to the maximum again by pumping in hydraulic fluid from a tank (7). As the pressure drop occurs according to a certain time function, it is possible to calculate the hydraulic pressure from the time elapsed since the beginning of the cycle. This obviates the need for continuous measurement of the hydraulic pressure. The invention may be advantageously used in synchronous switches.
